Direct current-light arc furnace

ABSTRACT

A direct current arc furnace, includes a graphite cathode; and a container forming a hearth with a hearth base surface and having a container bottom acting as anode. The container bottom includes a supporting copper-plated sheet steel base consisting of a steel sheet and a copper plating plated on the steel sheet; electrical connection means extending through the steel sheet to contact the copper plating to supply an anode current to the copper plating; and a refractory brick lining having a graphite content above the copper-plated sheet steel base with the copper-plated layer adjacent the brick lining. In a preferred embodiment the graphite content in the brick lining decreases from the vicinity of the copper-plated sheet steel base to the vicinity of the hearth base surface.

BACKGROUND OF THE INVENTION

The present invention is directed to a direct current arc furnace. Moreparticularly, it relates to a direct current arc furnace which has acathodically connected graphite electrode adjustable relative to ahearth and a container with a base forming an anode.

In direct current arc furnaces, in contrast to three-phase arc furnaces,it is possible to work with only one graphite electrode as cathode andone ground electrode as anode, which graphite electrode can be adjustedthrough the cover of the furnace. This results in lower constructioncosts with respect to the plant. Such direct current arc furnaces arealso distinguished by substantially lower electrode consumption as wellas by a longer service life of the refractory lining of the containerwall. With respect to energy the consumption is lower; moreover networkreactions (flickering) are noticeably reduced. Due to decreasedinductive influences the use of austenitic steel qualities can also bedispensed with to a great extent in the construction of the furnace.Another advantage of the direct current arc furnace consists in itslower noise emissions.

Certain problems are posed in the direct current arc furnace by theanodically connected bottom electrode forming the backplate electrodefor the cathodically connected graphite electrode which can be adjustedrelative to the hearth through the cover of the container. An iron corepenetrating through the base and through the refractory lining arrangedon the base was first provided for this purpose. However, the iron coreis subjected to a rapid melting away especially in melts with low carbonand high oxygen contents. Further, instead of an iron core with acomparatively large cross section, a plurality of steel rods wereprovided extending from an anodically connected steel plate arranged atthe base of the container up to the hearth base (DE-OS 34 09 255). Inthis respect the lining, i.e. the insertion or application of therefractory lining, poses familiar difficulties. Difficulties are alsoposed by subsequently driving the steel rods into the refractory lininguntil contacting the anodically connected base plate. Insofar as it hasbeen suggested to construct the area of the container base forming theanode so as to be exchangeable (DE-OS 35 35 692) corresponding problemsarose in the construction of the exchange element. Moreover, in bothcases the construction of the anode area remained limited to the centerof the hearth base.

Instead of the steel rods forming the anode it was also suggested toform the refractory base lining itself so as to be electricallyconducting by inserting stones encased in sheet metal or graphite orstones with a higher proportion of graphite. A copper insert in the formof rails or plates was provided as intermediate layer between the steelcontainer base and the refractory lining, the anode current beingapplied to this copper insert (DE-OS 35 34 750 and DE-OS 34 13 745). Avariant provides for a multiple-layer refractory lining of the containerbase having a plurality of layers of refractory electrically conductingstones and a refractory stamping mass arranged on the latter. Steel rodscontacting the uppermost stone layer are driven through the stampingmass (DE-OS 29 05 553). The refractory base lining can also be providedwith an anodically connected copper plate as underpinning. However, acopper plate itself is not suitable for taking over supportingfunctions. For this reason a sheet steel base is provided according tothe prior art which is provided with a cover of abutting copper sheetsegments which are connected with the sheet steel base by a plurality ofpins.

The construction of the container base itself as anode provesadvantageous to the extent that the current conduction is effected withthe greatest possible contact surface resulting in a low specificcurrent loading of the container base, specifically its refractorylining, which is reflected in an improvement of the service life of thebase. The manner in which the supporting sheet steel base is connectedwith the copper covering proves disadvantageous in this prior art. Forthis purpose a plurality of bore holes are to be introduced into thesheet steel base and into the copper sheet segments assigned to it witha matching hole pattern. The pins connecting the elements extend throughthese copper sheet segments. This manner of connecting the sheet steelbase and copper sheet segments is obviously very costly. Air gaps alsonecessarily remain between the sheet steel base and the copper coveringand between the copper sheet segments themselves as well as between thesupporting sheet steel base and the copper segments which also undergoan enlargement in the course of operation under the influence of thehigh operating temperature. This results in the risk that heavy metalproceeding from the insert will run under the copper covering. Therequired cooling of the base is accordingly impaired and ultimately alsothe life of the base.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide adirect current-light arc furnace with a copper covering, which avoidsthe disadvantages of the prior art.

In keeping with this object and with others which will become moreapparent hereinafter, one feature of the present invention resides,briefly stated, in a direct current-light arc furnace which, inaccordance with the present invention, includes a graphite cathode; anda container forming a hearth with a hearth base surface and having acontainer bottom acting as anode. The container bottom includes asupporting copper-plated sheet steel base consisting of a steel sheetand a copper plating plated on the steel sheet; electrical connectionmeans extending through the steel sheet to contact the copper plating tosupply an anode current to the copper plating; and a refractory bricklining having a graphite content above the copper-plated sheet steelbase with the copper plated layer adjacent the brick lining.

The container bottom having copper-plated sheet steel base according tothe invention is a simple compact structural component part which isaccordingly inexpensive. The structural component part combines adesired greatest possible contact surface for the current conductionwith an avoidance of the defects which encumber the sheet steel baseswhich are provided, according to the prior art, with a copper coveringin the form of rails, plates or sheet metal blanks (segments).

The large contact surface for the current conduction makes it possibleto provide in the lining proceeding from the base a decreasingproportion of structural component parts, particularly graphite, whichbring about the electrical conductivity of the refractory lining. Theservice life of the refractory lining is accordingly increased. With acorresponding objective, a refractory lining which is substantially freeof the structural component parts bringing about the electricalconductivity can be provided in the center of the base lining. In apreferred embodiment an layer of graphite inserted between thecopper-plated sheet steel base and the refractory lining arranged on thelatter improves the current conduction from the base into the liningunder which the base serves as a support. Of course, a copper alloyplating with a high proportion of copper can also be provided for thesupporting structural component part of the container base instead ofcopper plating.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the arc furnace in section;

FIG. 2 shows a section from the container base in enlarged

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The furnace includes the container 21 with a container bottom 22 and thecover 23 which can be lifted from it. The container 21 is supported in asupporting construction 11 integrated in the furnace platform so as tobe tiltable (double arrow A). The container bottom 22 havingcopper-plated sheet steel base 221, 222 is detachably flanged on (212,32, 223) at the container casing 211 with the inclusion of insulation31.

The container 21, is provided with a hearth 24 with the hearth basesurface 241, which is lined, i.e. provided with a refractory bricklining. Concretely, the wall is lined in the vicinity of the hearth 24with magnesite stones 41 and the copper-plated sheet steel base with aplurality of layers 42, 43 and 44 of magnesite stones containinggraphite, the first layer 42 of which has the highest proportion ofgraphite, approximately 20%. The next layer 43 contains approximately10% and the third layer 44 contains less than 10% graphite with acentral region 43', 44' in which graphite-free magnesite stones areinserted at least in the upper stone layers. Intermediate spacesremaining between the brick lining 41 of the wall and the brick lining42, 43, 44 of the base are filled up with refractory stamping mass 46. Agraphite layer 47 is inserted between the container copper-plated sheetsteel base 221,222 and the lowest layer 42 of the brick lining.Refractory, graphite containing stamping mass can then be applied to theuppermost stone layer 44; at least the uppermost layer 44 itself canalso have refractory stamping mass. The container wall above the hearth24 is formed by cooling elements, e.g. elements 213 through whichcooling water flows, or by spray cooling elements 213'. An airconducting plate 224 is provided below the base 221,222 for cooling thebase.

The melt 61 with the slag 62 located on it is situated in the hearth 24.The combustion point 611 is formed in the center.

A graphite cathode 71 is guided in a central passage 231 in thecontainer cover 23 in such a way that it can be raised and lowered(double arrow B). The anode current is applied to the copper plating 222of the container base 22 via the electrical connections 226, 226'extending through the sheet steel base 221.

In the shown furnace the electrically conducting magnesite stones arecut out and the electrically nonconductive magnesite stones 43', 44' areinserted in the center of the base lining 42, 43, 44 in the upper layers43, 44.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in adirect current-light arc furnace, it is not intended to be limited tothe details shown, since various modifications and structural changesmay be made without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:
 1. A direct current arc furnace,comprising a graphite cathode; anda container forming a hearth with ahearth base surface and having a container bottom, wherein saidcontainer bottom includes a supporting copper-plated sheet steel baseconsisting of a steel sheet and a copper plating on said steel sheet;electrical connection means extending through said steel sheet tocontact said copper plating to supply an anode current to said copperplating; and a brick lining of refractory material arranged on saidcopper-plated sheet steel base, said copper plating being positionedbetween said brick lining and said steel sheet.
 2. A direct current arcfurnace as defined in claim 1, wherein said brick lining is composed ofgraphite-containing material having a graphite content.
 3. A directcurrent arc furnace as defined in claim 2, wherein said graphite contentin said brick lining decreases from the vicinity of said copper-platedsheet steel base to the vicinity of said hearth base surface.
 4. Adirect current arc furnace as defined in claim 3, wherein a graphiteproportion in said brick lining in the vicinity of said copper-platedsheet steel base is 20%, while a graphite proportion in said bricklining in the vicinity of said hearth base surface is below 10%.
 5. Adirect current arc furnace as defined in claim 1, further comprising agraphite layer located between said copper-plated sheet steel base andsaid brick lining.
 6. A direct current arc furnace as defined in claim1, wherein said brick lining has a central region substantially free ofgraphite.
 7. A direct current arc furnace as defined in claim 1, whereinsaid copper plating has a maximum thickness of 10 mm.
 8. A directcurrent arc furnace as defined in claim 1, wherein said container has acover, said graphite cathode being adjustably positionable relative tothe hearth base surface through said cover of said container.